diff --git a/src/layers/normalise.jl b/src/layers/normalise.jl
index 88c06673..c0d4aabf 100644
--- a/src/layers/normalise.jl
+++ b/src/layers/normalise.jl
@@ -114,6 +114,8 @@ BatchNorm(chs::Integer, λ = identity;
             zeros(chs), ones(chs), ϵ, momentum, true)
 
 function (BN::BatchNorm)(x)
+  size(x, ndims(x)-1) == length(BN.β) ||
+    error("BatchNorm expected $(length(BN.β)) channels, got $(size(x, ndims(x)-1))")
   λ, γ, β = BN.λ, BN.γ, BN.β
   dims = length(size(x))
   channels = size(x, dims-1)